Heusler Thermoelectrics

RYAN NEED

UNIVERSITY OF CALIFORNIA SANTA BARBARA

MATRL 286G, SPRING 2014

Heusler Compounds

Heusler Compounds

Half Heusler, XYZ(e.g. TiCoSb)

Sb Ti

Co

Heusler Compounds

Half Heusler, XYZ(e.g. TiCoSb)

Sb Ti

Co

Full Heusler, XY2Z(e.g. TiCo2Sb)

Sb Ti

Co

ThermoelectricDevices

Images from: J-F Li, W-S Liu, L-D Zhao, M Zhou, High-performance nanostructured thermoelectric materials, NPG Asia Mater. 2 4 (2010) 152-158.

Images from: J-F Li, W-S Liu, L-D Zhao, M Zhou, High-performance nanostructured thermoelectric materials, NPG Asia Mater. 2 4 (2010) 152-158.

ThermoelectricDevices

Heusler Compounds

ThermoelectricDevices

The goal of this talk…

is to understand where these two overlap.

Points of inquiry

1. What material properties make a good thermoelectric?

• Derivation of thermoelectric figure or merit, ZT• Relationships between electronic and thermal

properties

Points of inquiry

1. What material properties make a good thermoelectric?

• Derivation of thermoelectric figure or merit, ZT• Relationships between electronic and thermal

properties

2. How do Heusler alloys meet these criteria?

• Electron count rules for semiconducting behavior• Unit cell complexity and alloying for phonon scattering

Points of inquiry

1. What material properties make a good thermoelectric?

• Derivation of thermoelectric figure or merit, ZT• Relationships between electronic and thermal

properties

2. How do Heusler alloys meet these criteria?

• Electron count rules for semiconducting behavior• Unit cell complexity and alloying for phonon scattering

3. Can we design nanostructures to improve Heusler TEs?

• Nanoscale grain sizes through ball milling and SPS• Half Heusler matrix with full Heusler nanoparticles

Points of inquiry

1. What material properties make a good thermoelectric?

• Derivation of thermoelectric figure or merit, ZT• Relationships between electronic and thermal

properties

2. How do Heusler alloys meet these criteria?

• Electron count rules for semiconducting behavior• Unit cell complexity and alloying for phonon scattering

3. Can we design nanostructures to improve Heusler TEs?

• Nanoscale grain sizes through ball milling and SPS• Half Heusler matrix with full Heusler nanoparticles

What material properties do we need to considerfor a thermoelectric device?

What material properties do we need to considerfor a thermoelectric device?

What do we want this thermoelectric device to do?

What material properties do we need to considerfor a thermoelectric device?

What do we want this thermoelectric device to do?

To maximize output power or temperature gradient

What material properties do we need to considerfor a thermoelectric device?

What do we want this thermoelectric device to do?

To maximize output power or temperature gradient

QC

QH

What material properties do we need to considerfor a thermoelectric device?

What do we want this thermoelectric device to do?

To maximize output power or temperature gradient

QC

QH

QC = PeltierCooling

What material properties do we need to considerfor a thermoelectric device?

What do we want this thermoelectric device to do?

To maximize output power or temperature gradient

QC

QH

QC = Joule

HeatingPeltierCooling −

What material properties do we need to considerfor a thermoelectric device?

What do we want this thermoelectric device to do?

To maximize output power or temperature gradient

QC

QH

QC = Joule

HeatingThermalDiffusion

PeltierCooling − −

What material properties do we need to considerfor a thermoelectric device?

What do we want this thermoelectric device to do?

To maximize output power or temperature gradient

QC

QH

QC = Joule

HeatingThermalDiffusion

PeltierCooling − −

What material properties do we need to considerfor a thermoelectric device?

What do we want this thermoelectric device to do?

To maximize output power or temperature gradient

QC

QH

QC = Joule

HeatingThermalDiffusion

PeltierCooling − −

The key material properties are inversely relatedthrough carrier concentration.

The key material properties are inversely relatedthrough carrier concentration.

Image from: G.J. Snyder, E.S. Toberer, Complex thermoelectric materials, Nat. Mater. 7 (2008) 105-

114.

The key material properties are inversely relatedthrough carrier concentration.

We want a degenerate semiconductor or dirty metal with a complex lattice

for optimal ZT and device performance.

Image from: G.J. Snyder, E.S. Toberer, Complex thermoelectric materials, Nat. Mater. 7 (2008) 105-

114.

The key material properties are inversely relatedthrough carrier concentration.

Points of inquiry

1. What material properties make a good thermoelectric?

• Derivation of thermoelectric figure or merit, ZT• Relationships between electronic and thermal

properties

2. How do Heusler alloys meet these criteria?

• Electron count rules for semiconducting behavior• Unit cell complexity and alloying for phonon scattering

3. Can we design nanostructures to improve Heusler TEs?

• Nanoscale grain sizes through ball milling and SPS• Half Heusler matrix with full Heusler nanoparticles

Valence precise half Heusler compoundscan be semiconductors.

Sb Ti

Co

Image from: H.C. Kandpal, C. Fesler, R. Seshadri, Covalent bonding and the nature of band gaps in some half-Heusler

compounds, J. Phys. D 39 (2006) 776-785.

Example: TiCoSb

Valence precise half Heusler compoundscan be semiconductors.

Sb Ti

Co

Image from: H.C. Kandpal, C. Fesler, R. Seshadri, Covalent bonding and the nature of band gaps in some half-Heusler

compounds, J. Phys. D 39 (2006) 776-785.

Example: TiCoSb

Valence precise half Heusler compoundscan be semiconductors.

X: Ti → Ti4+

(Ar)Y: Co → Co4-

(Ga)Z: Sb → Sb

X gives up its electrons and formsa covalent zinc-blende YZ sublattice.

Sb Ti

Co

Image from: H.C. Kandpal, C. Fesler, R. Seshadri, Covalent bonding and the nature of band gaps in some half-Heusler

compounds, J. Phys. D 39 (2006) 776-785.

Example: TiCoSb

X: Ti → Ti4+

(Ar)Y: Co → Co4-

(Ga)Z: Sb → Sb

Valence precise half Heusler compoundscan be semiconductors.

18-electron half Heusler compoundsare electronically identical to common III-V

systems.

Image from: T.Graf, C. Fesler, S.S.P. Parkin, Simple rules for the understanding of Heusler compounds, Prog. Solid State Chem. 39 (2011) 1-50. Values from: H. Hohl, A.P. Ramirez, C. Goldmann, G. Ernst, B. Wolfing, E. Bucher, Efficient dopant for

ZrNiSn-based thermoelectric materials, J. Phys.: Condens. Matter 11 (1999) 1697-1709.

Atomic disorder can be used to scatter phononsby alloying on the X, Y, and Z sites.

Image from: T.Graf, C. Fesler, S.S.P. Parkin, Simple rules for the understanding of Heusler compounds, Prog. Solid State Chem. 39 (2011) 1-50. Values from: H. Hohl, A.P. Ramirez, C. Goldmann, G. Ernst, B. Wolfing, E. Bucher, Efficient dopant for

ZrNiSn-based thermoelectric materials, J. Phys.: Condens. Matter 11 (1999) 1697-1709.

Atomic disorder can be used to scatter phononsby alloying on the X, Y, and Z sites.

Heavily alloy X sitewith large mass contrast (XX’NiSn)

X: Ti → ZrxHfyTi0.5

κ: 9.3 W/mK → 3-6 W/mK

Image from: T.Graf, C. Fesler, S.S.P. Parkin, Simple rules for the understanding of Heusler compounds, Prog. Solid State Chem. 39 (2011) 1-50. Values from: H. Hohl, A.P. Ramirez, C. Goldmann, G. Ernst, B. Wolfing, E. Bucher, Efficient dopant for

ZrNiSn-based thermoelectric materials, J. Phys.: Condens. Matter 11 (1999) 1697-1709.

Atomic disorder can be used to scatter phononsby alloying on the X, Y, and Z sites.

Heavily alloy X sitewith large mass contrast (XX’NiSn)

X: Ti → ZrxHfyTi0.5

κ: 9.3 W/mK → 3-6 W/mK

Lightly dope on the Z siteto introduce carriers (XX’NiSn:Sb)

Z: Sn → Sn1-δSbδ

σ: 100 S/cm → 1200 S/cm

However, phonons cover a wide range of wavelengthsand require a multi-length scale scattering approach.

Image from: K. Biswas, J. He, I.D. Blum, C-I Wu, T.P. Hogan, D.N. Seidman, V.P. Dravid, M.G. Kanatzidis, High-performance bulk thermoelectrics with all-scale hierarchical architectures, Nat. Lett. 489 (2012) 414-418.

Points of inquiry

1. What material properties make a good thermoelectric?

• Derivation of thermoelectric figure or merit, ZT• Relationships between electronic and thermal

properties

2. How do Heusler alloys meet these criteria?

• Electron count rules for semiconducting behavior• Unit cell complexity and alloying for phonon scattering

3. Can we design nanostructures to improve Heusler TEs?

• Nanoscale grain sizes through ball milling and SPS• Half Heusler matrix with full Heusler nanoparticles

Nanoscale grain sizes impede mid-wavelength phonons,reduce thermal conductivity, and improve ZT.

Images from: X. Yan, G. Joshi, W. Liu, Y. Lan, H. Wang, S. Lee, J.W. Simonson, S.J. Poon, T.M. Tritt, G. Chen, Z.F. Ren, Enhanced thermo-electric figure of merit of p-type half-heuslers, Nano Lett. 11 (2011)

556-560.

Zr0.5Hf0.5CoSb0.8Sn0.2

Half Heusler matrices with full Heusler nanoparticlesalso show reduced thermal conductivity and improved ZT.

Image from: J.E. Douglas, C.S. Birkel, M-S Miao, C.J. Torbet, G.D. Stucky, T.M. Pollock, R. Seshadri, Enhanced thermoelectric properties of bulk TiNiSn via formation of a TiNi2Sn second phase, Appl. Phys. Lett. 101 (2012) 183902.

Half Heusler matrices with full Heusler nanoparticlesalso show reduced thermal conductivity and improved ZT.

Image from: J.E. Douglas, C.S. Birkel, M-S Miao, C.J. Torbet, G.D. Stucky, T.M. Pollock, R. Seshadri, Enhanced thermoelectric properties of bulk TiNiSn via formation of a TiNi2Sn second phase, Appl. Phys. Lett. 101 (2012) 183902.

High thermal conductivity still limits ZTin state-of-the-art Heulser thermoelectric compounds.

MATERIAL κ [W/mK] ZT (Meas. Temp) [Ref.]

TiNiSn (n-type) 4-5 0.35 (740K) [1]

Hf0.5Zr0.5NiSn 3 0.9 (960 K) [2]

Zr0.25Hf0.25Ti0.5NiSn0.998Sb0.002 3 1.4 (700 K) [2]

TiCoSb (p-type) 6-12 0.04 (780 K) [1]

ZrCoSb0.9Sn0.1 7-10 0.45 (958 K) [2]

Zr0.5Hf0.5CoSb0.8Sn0.2 3.6-4.1 0.8 (1000 K) [2]

SnSe 0.3 - 0.7 2.6 (932 K) [3]

Values from: [1] C.S. Birkel, W.G. Zeier, J.E. Douglas, B.R. Lettiere, C.E. Mills, G. Seward, A. Birkel, M.L. Snedaker, Y. Zhang, G.J. Snyder, T.M. Pollock, R. Seshadri, G.D. Stucky, Rapid microwave preparation of thermelectric TiNiSn and TiCoSb half-Heusler compounds, Chem. Mater. 24 (2013) 2558-2565. [2] T.Graf, C. Fesler, S.S.P. Parkin, Simple rules for the understanding of Heusler compounds, Prog. Solid State Chem. 39 (2011) 1-50. [3] L-D. Zhao, S-H Lo, Y. Zhang, H. Sun, G. Tan, C. Uher, C. Wolverton, V.P. Dravid, M.G. Kanatzidis, Ultralow thermal conductivity and high thermoelectric figure of merit in SnSe crystals, Nat. Lett. 508 (2014) 373-377.